Soluble growth factors play a vital role in virtually all tissue development and regeneration processes, and inductive growth factors are critical components of many emerging tissue engineering strategies. However, approaches used to design biomaterials have not yet achieved a high level of control over growth factor signaling during development of engineered tissues. We propose to develop a new class of biomaterials capable of locally regulating growth factor signaling. Our approach uses low molecular weight ligands, including peptide and oligonucleotide ligands, to specifically and reversibly sequester growth factors upon and within biomaterials. We hypothesize that these specific, variable affinity interactions will control local growth factor availability, resulting in up- or down-regulated growth factor activity. This approach will initially be used to regulate the effects of vascular endothelial growth factor (VEGF) and fibroblast growth factor-2 (FGF2) on endothelial cells in 2-dimensional and 3-dimensional culture environments. This signaling system is ideal for the proposed studies, as VEGF and FGF2 have well-characterized and pronounced effects on survival, proliferation, and differentiated function of endothelial cells in vitro and in vivo. Furthermore, regulation of endothelial cell behavior has significant implications for clinical applications that require highly regulated vascular tissue growth, including regenerative medicine. We specifically aim to: 1) develop and characterize tailored cell culture substrates for localized, controlled sequestering of FGF2 and VEGF; 2) characterize the combinatorial influence of non-covalent growth factor sequestering and cell adhesion on growth factor signaling and, in turn, survival, proliferation, and organization of endothelial cells in vitro; and 3) scale the growth factor sequestering approach to a well-defined hydrogel matrix, and characterize regulated growth factor signaling during capillary morphogenesis and ex vivo aortic sprouting. Alkanethiolate self-assembled monolayer substrates and PEG hydrogels will be used as initial model biomaterials to address the hypothesis guiding this proposal. Cells and proteins exhibit little or no intrinsic interaction with these materials, and they therefore serve as well-defined model systems to explore affinity- based growth factor regulation. We anticipate that the proposed approach can ultimately be applied to a broad range of common biomaterials, and may represent a new direction in biomaterials design. Development of all tissue types requires the coordinated action of particular proteins called growth factors. Current strategies that attempt to engineer new tissues are unable to control the effects of growth factors, and it is therefore difficult to mimic tissue development and form functional tissues for transplantation. This proposed research program will develop a new class of materials that can be used to control the effects of growth factors during engineered tissue development, particularly vascular tissue development.